Telephone system



Feb. 7, 1928. 1,658,450

. c. E. LOMAX TELEPHONE SYSTEM I Filed an. 26, 1925 3 Sheets-Sheet l y. :IEXEHANEE H ER? km Q5 o h: I

IITU' EH70?" Clarence E. Lumax Feb. 7, 1928.

C. E. LOMAX TELEPHONE SYSTEM Filed Jan. 26, 1925 3 Sheets-Sheet 5 MHZ IUXE ImZ/xkm Clare cEE Lumax HIT- tails and thesev will all be explained Patented Feb. 7, 1928.

uuirsos'rarss PATENT OFFICE.

CLARENCE E. LOMAX, OF CHICAGO, ILLINOIS, ASSIGNOR, BY IVIESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLENDIS, A CORPORATION OF DELA- WARE.

Application filed January Thepresent invention relates to telephone systems in general, but is concerned more particularly with telephone systems in which both main exchanges and branch exchanges are employed; and the broad general object,

may be also the night watchman, or some other similar employee.

According to one feature of the invention, a new and improved single-digit rotaiyconnector switch of moclern clesign 1s provided for completing connections w th the various groups ot' main to branch ex change trunk lines. This switch incorpon ates, among other things, a novel circuit arrangement for preventing the premature application of ringing current to a called line. Another object is the provision of circuit arrangements in a cord circuit such that one of the strands of the cord circuit is normally open as regards the passage of direct current and remains open after the plug has been inserted into a jack and is closed only by the operation of'the. ringing key by the operator, which of course takes place'i'n'the usual course of events when, the operator rings the called substation. This open point is placed in the strand of tie cord circuit v:ifivhich the line switch of the called substation otherwise might operate upon the insertion of the plug into the jack before the bridge cut-oil? relay of the line switch can operate to disconnect the line relay.

The other objects and features of this case are concerned mainly with the circuit defully hereinafter;

Referring now to the drawings comprisr ing Figs. 1,

1 shows equip ment located n the autom c main exchange and Figs. and 3 slmw equipment located in the automatic private branch exchange,

rnnnrnonn 'sYs'rnM. a UE 2s, i925. Serial No. 4,691. i-

which, however, is not strictly automatic for falls incoming from the main exchange, but may be, from this standpoint, considered as a combined automatic and manual privatebranch exchange. r

The apparatus shown in Fig. 1 comprises the single-digit rotary connector C which is accessible to the selectors at the main eX-y change and which has access to-the two-Way trunk line TL, and others, leading to the branch exchange. Calls originating in the branch exchange and intended torthe main exchange are completed over trunk lines, such as the trunk line TL, and, when completed over the trunk line TL, are extended to first selector switches through the medium of the line switch LS. i

The equipment shown in Fig. 2 comprises the trunk circuit TC, through which the calls incoming to the branch exchange from the main exchange are-completed, and the cord circuit CC which the operator uses to extend incomingcalls to the local lines.

This drawing shows also the night position at which the key circuit KG is located and through which the calls incoming to the branch exchange trom the main exchange are completed during the night when the night key NK individual to the trunk circuit TC is thrown by the operator at the day position when she leaves. This drawing shows also the holding circuit HG which is provided to hold up theestablished connection when. the trunk'line TL is seized by a local selector'when a call originating in the branch exchange is inte-ndedfor the Sub scriber at the main exchange.

Fig. 3 shows the substation A whose line extendsto the private branch exchange and terminates there in the line switch LS, which extends the line of substation A,-;when calling, to an idle first selector. The line of substation A may be seized by local connectors-or by the operator at the day position who, for this purpose, may insert the plug of cord circuit into] the jack J. Fig. 3 shows also the line switch LS which is in-* dividual'to the hey circuit KC at the night;

In order to complete the general" descrip-' tion of the drawings, it maybe pointed out that the connector C, Fig. 1, is mechanically" ot the usual vertical and rotary type of tion only, and are advanced upon the back stroke of the associated stepping .magnet rather than upon the front stroke.

It will now be assumcdthat a subscriben in the main exchange desires to converse with the subscriber at substation A in the branchiexchange. It will be assumed further that when the callingsubscriber at the main exchange removes his receiver and dials the preliminary digits in the number ot-the branch-exchange,aselector under his control seizesthe connector C, Fig. 1, at-the bank contacts-9193.

VVhenthe connector C is seized, line relay 3, whichisbridged acrossthe line conductors of the connector through the normally closed contacts controlled by armatures 2d and 23 of the back bridge relay 2, pulls up over the calling loop and closes at armature 25 a circuit forrelease relay 4. Release relay-energizesand prepares at armature '28 a circuit for vertical magnet 15,-at the same time-opening a point-in the circuit of release magnet 10. At armature 27, relays places ground 'on the local holding conductor 97 so as to furnish holding ground for various relays-of the switch. At armature 26, relay l-places ground-on the release trunk con ductor '95, thereby establishing the usual holding circuit for the seizing selector to prevent it and the other switches involved in the connection from releasing prematurely.

It Will be noted that the release trunk conductor95'and the local holding conductor 97 are normally connected togetherthrough the resting contact and armature 29 of the se ries relay 5. The reason for this tie between these two conductors and the provision of contacts for severing it will be explained fully hereinafter.

When the calling subscriber dials the-next digit in the desired number, line relay 3 deenergizes :a corresponding number of times and,=upon each deenergization, closes at armature 25a circuit through armature 28 and its working contact, series relay '5, and armature 89 and its resting contact for vertical :magnet :15. 'By the operation of vertical magnet 15, the wipers 41-43 are raised step by step and come to rest opposite the desired level of bank contact-s. Relay 5 is energizedin series with vertical magnet 15 upon the'first impulse of current being'delivered to the'latter, and, being slowacting, maintains its armature attracted throughout the seriesof impulses. Atarmature 29, relay ;5 disconnects conductor 97 from con- I ductorf95, butthisdoes not have any particular utility at this time. At armature 30 relay 5 opens a point in the circuit o1 rotary magnet 13 and prepares a circuit forstepping relay 7 which is completed through the interrupter contacts 1d at the-oil normalcontacts 12 as soon as-these .contacts close, as they do upon the first vertical step of the switch. Responsive to the closure of: this circuit, stepping relay 7 energizes and completes a locking circuit for itself at armature 3a and armature l9 and its resting con tact, and atarmature 35 prepares a circuitfor rotary -m-agnet 13.

At the end of the vertical movement, the slow acting series-relay 5 falls back and completes at armature 30 a circuit from the grounded holding conductor .97through ar- 1naturc'37 and its resting contact, .and'the working contact and armature for rotary magnet 13. Rotary magnet 13 responsivelj energizes and advances the wipers l-143 into engagement with the first set of bank contacts in the level opposite which they were previously raised, and, near the end of its stroke, opens at armature 1a the circuit of stepping relay 7 Relay 7 accordingly dcenergizcs and opens at armature 34 its previously closed locking circuit and opens at armature 35 the circuit of the rotary magnet. When this occurs, the rotary magnet deenergizes and closes its interrupter contacts :14. again.

From this point, the operation depends upon whether the trunk line terminating in the first setof contacts is busy or idle. Ifit is busy, switching relay 8, which is connectedto the grounded conductor 97 on one side and'to the circuitof the stepping relay 7 :on the other side, is short circuited and does not energize. Stepping relay 7, at this time, energizes from the ground potential encountered upon the busy test contact by test wiser 42 and extended to the circuit of relay 7 througharmature 36 otrelay 8 and its resting contact. At armature 341, relay '7 againcompletes its-locking circuit, and at armature 85 it again closes the circuit of the rotary magnet, whereupon rotary magnet 13 energizes again and advances the wipers of the switch into engagement with the next set of bank contacts.

This alternateoperation of stepping relay 7 and rotary magnet '13 continues as described until-an' idle trunk is reached, which trunk, it will be assumed, is the onecomprising conductors 4-7-4-9. hen this idle trunk is reached, switching relay 8. being no longer short circuited, energizes in series with stepping relay 7. stepping relay 7, however. is not operatively energized at this time, on account of the relatively high resistance of switch ng relay 8. Upon enen gizing, switching relay 8 inserts the resistance 16 in series with vertical magnet 15 so as to prevent any further operation of the ill) latter in case the calling subscriber should again manipulate his calling device and also to preventoperation of the vertical magnet 15 when the calling subscriber replaces his receiver. The operating circuit is not entirely opened, however, owing to the fact that it is desired to have the series relay 5 operate again when the calling subscriber replaces his receiver, as will be hereinafter pointed out. At armature 37, relay 8 disconnects the grounded locking conductor 97 from armature 30 of series relay. 5 so as to prevent this relay from closing a circuit for stepping relay 7 and short circuiting the switching relay 8 when it subsequently energizes again. At armature 36, relay 8 disconnects test wiper 4-2 from the testing circuit and connects it to grouno instead. hen this occurs, the combined switching and cut-oil relay 61 of the line switch LS energizes through bank contact 15, private normal conductor 48, relay G1, and rotary magnet 63 to battery. lfhen this occurs, relay G1 pulls up and disconnectsconductors 17 and 49 from relay ":2 and grounth respectively, but the relay does not operate enough to connect up the wipers of the line switch, owing to the usual interlocking device (not shown) between the armature proper of relay 61 and that of line relay 62.

In the branch exchange, the high resistance polarized relay 103, which is bridged across conductors 17 and 419 of the trunl; line TL through armature 110 and its resting contact, now deenergizes due to the removal of battery ground from the conduct-01's of the trunk line TL at the line switch LS, as above described. Upon deenergizing, relay 103 permits the spring as-, sociated with the armature 111' to pull the armature into engagement with the associated contact, thereby closing a circuit for relay 105, which includes the resting contact and armature 109 of relay102. Relay energizes; connects up conductor 1'? to th'eti p spring of the jack J at armature 114-; places a shunt around the resting contact, and armature 109 at armature 115; and at armaturellfi disconnects release trunlr con ductor 117 from cut-oil relay 102and connects it to ground instead, thereby making the trunk line TL busy to the branch exchange selectors having access to it.

Returning new to the connector C in the main exchange, as a still further result of the energization of switching relay 8, it removes at armature 38 the shunt from around the wiper connecting relay 9, responsive which relay 9 energizes and connects up the wipers 11 and 43. at armatures 39 and 10, Relay 9 is rather stii'lly adjusted and its inclusion int-o the circuit in series with relay 8 is delayed as long as possible by adjusting armature 38 to break just before the armature proper of the relay has completed its stroke. These two things combined (in ad dition to the arrangement whereby armature 36 operates to ground wiper 12 practically as soon as the armature proper of the relay starts to move) result in the delay of the connecting up of wipers 11 and 43 until the combined switching and cut-off relay 61 of the line switch LS has had time to energize responsive to the grounding of test wiper 412 and disconnect the line relay 62 and ground from conductors a"? and l9. This precaution is taken, it may be pointed out, owing to the fact that the connecting up of the wipers ell and 13 and the grounding of the test wiper 42, at very nearly thesa'me time (which would ocur if only one relay were employed to perform the function of both relays 8 and 9) might result, in a large percentage of the connections, in the pre mature tripping of the ring cut-oil relay 6 from the ground on conductor 49 and in the en-ergization of line relay of the line switch from the grounded generator lead and over wiper 43, the conductors a la'nd 19 being reversed between the trunk line TL proper and the connector banks for a purpose to be later explained.

Ringing current is now intermittently projected out over wiper 13, bunl: contact and conductor 1? of the trunk line TL to the trunk circuit TC, at which point the polarized relay 103 and the lower winding of relay 101 (with the condenser 117 in series with it), are both bridged across the conduc tors of the trunk line TL. The impedance of the polarized relay 103, however, is so high that very little ringing current passes through it. The ringing current which passes through the bridge including the lower winding of relay 101 and condenser 117' is provided with a return path through armature and its resting contact, conductor l9, bank contact eta, wiper 11, working contact and armature 39, arn'iature 31 and its resting contact, andthe upper winding of the ring cut-oil relay 6 to battery. Relay 101 energizes responsive to this ring ing current and closes a locking circuit for its upper winding at armature 106. At

armature 107, relay 101 closes a circuit through the lower spring and its upper con tact of night key NK for the answering lamp 118.

Since the polarized relay 103 is bridged across the conductors Ol 'lllG trunk line TL, it energizes from the battery supplied to conductor 49 through the upper winding of the ring cut-oil relay 6 of the connector O and ground supplied to conductor at over the ringing lead, The ring cut-oil relay or the connector is not energized in series with relay 103 owing tothe relatively high resistance of the latter. Relay 103 does not operate its armature 111 to the-position shown in the drawing owing to the f actthatit is l energized ina direction. opposite to that in; which it lsnormally energized and attempts.

the-reversal in the trunk line at the banks of the connector C. Otherwise, the relay 103 would energize again as soon as the wipers of the connector (1 are connected up by relay 9, as above pointed out.

When the operator perceives the lighted condition of the answering lamp 118, she inserts the answering plug of an idle cord cir cuit, for example, the plug 1 of the cord circuit CG, into the jack J. Responsive to this, the springs 118 of the jack J close, thereby closing a circuit for relay 104-. Relay 10 1 energizes and places a second shunt around the resting contact and armature 109 at armature 113, and at armature 112 closes a circuit for cut-off relay 102. Cut-011' relay 102 energizes; opens the locking circuit of relay 101 at armature 108; opens the initial circuit of relay 105 at armature 109, leaving it operated through armature; 113 and 115 in multiple; and at armature 110 disconnects relays 101 and 103 from in bridge of the conductors 17 and 19. Relay 101 now deenergizes and opens the circuit of the lamp 118 at armature 107.

As a further result of the insertion of the i; plug P into the jack J, the tip and ring.

conductors of the plug P are connectedto the tip and ring conductors of the jack J. Accordingly, the bridged supervisory relay 123, which is bridged across the talking strands of the cord circuit through armature 127 and its resting, contact, is now bridged across the conductors 17 and 49 of the trunk line TL. As a result, the ring cut-ofi relay 6 of the connector is energized over its upper winning. At armature 32, ring cut-oil relay 6 closes locking circuit for its lower winding, and at arinatures 31 and 33, it disconnects the wipers 41 and 13 from its own upper winding and from the ringing lead and connects them instead to the back bridge relay 2. Accordingly, back bridge relay 2 now energizes over the trunk line TL and through the bridged relay 123 in the cord circuit CC; and closes at armature 18 a circuit for relay 17, which relay energizes; places a shu t around armature 27 and its working contact of relay 1 at armature 21; and opens a point. in the circuit of release magnet at armature 2 1.

At armatures-2 i and 23, relay 2.reverses the incoming line conductors 04-. and 96 as regards-their connections with the windings otline relay 3, thereby reversing the direction of the current flow in the calling loop. This reversal in the direction of the current Lasagna;

like operations.

Tnthe cord circuit CC, supervisory relay 123 is energized in seriesfirstwith ring out.

off relay 6, and then. with back bridge relay 2. Upon energizing, relay;123removesre+ sistance 126 from in shunt of relayi122; atv armature 127, and atarmature 128 closes:- a

scriber at substation A, the operator tests for the busyor idle condition of the'desired line bytapping the tip of the plug P against the sleeve of the jack J. If the desired line is busy, there is a ground potential upon the sleeve of the jack J and a circuit is closed through the tip of th'eplug 'P, springs of the key K, resting contact and armature 130, upper left springs of the key K, common test conductor 132, high resistance 137, and the tertiary winding of the operators induction coilto battery. Accordingly, the operator hears a click in her receiver R each time the tip of the plug P is touched against the sleeve of the jackJ, and. another click each time the connection is broken'between the two. In this case, the operator informs the calling subscriber that the desired line is, for the time being, inaccessible and the calling subscriber replaces his receiver with the result that the established connection is broken.

Assuming now that the'desired line is-idle when called, there is no ground potential on the sleeve of the jack J, but ratherabattery potential on this sleeve through the re lay 211 of the line switch LS, and the-associated stepping magnet. Accordingly, the operator hears no click when she tests the condition of the line and sheinserts the plug P into the jack J. lVhen this occurs, theupper contacts of 'the jack J placeground on the sleeve of the jack J, thereby closing a circuit over private normal conductor 202 for relay 211 of the line switch LS. Relay 211 accordingly operates far enough to disconnect the associated line relay 212 and the ground from the conductors of the desired. line, but does not operate any turther'onao' count or the previously mentionedinterloclo ing device between the armatures of the two relays of the line switch.

The operator now throws the key K into ringing position, thereby applying ringing The operator now con flow inthecallingloop .cloesnothave anyf particularutility as regards the-actualtransfer of talking: current, but may be'usediiin certain instances to operate meters and. for.

current to the called line to ring the bridged bell at the substation A.

It will be noted that the upper strand of the cord circuit CC is normally open as regards the passage of direct current, this strand being closed through the condenser 125 to permit the operator to converse with the calling subscriber when she throws her listening key K. Accordingly, there is no danger of the line switch on the called line being operated responsive to the insertion of he plug P into the jack, as might occur if the condenser 125 were shunted.

When the key K is thrown into ringing position, the called substation is signalled in the usual manner and, in addition, the circuit is closed at the upper right contacts of the key K for relay 12 1, Which energizes and locks itself to the sleeve conductor of the plug P at armature 131 and at armature 129 connects the supervisory relay 122 across the open point in the upper strand of the 'cord circuit preparatory to furnishing talking battery to the called substation. Relay 124 also opens the above mentioned busy test circuit at armature 130.

When the subscriber at substantion A removes his receiver, a direct current bridge is placed across the conductors of his line through the receiver, transmitter, and calling device. Since the plug P is now in the jack J, the placing or". the direct current bridge across the conductors of the line of substation A results in the placing of direct current bridge across the strands of the cord circuit CC in multiple with the supervisory bridge which includes the armature and contact of relay 122 and the supervisory relay 123. The series supervisory control relay 122 is included in the circuit in series with the bridge at the called substation, as it is now shunted around the condenser 125 through the working contact and armature 129 of relay 12a. Accordingly, relay 122 energizes in series with the called line and disconnects relay 123 from in bridge of the talking strands of the cord circuit. Relay 123 now deenergizes and extinguishes the supervisory lamp 121 at armature 128, thereby giving answering supervision to the branch exchange operator. As a further result of the deenergization of relay 123, it connects the resistance 1 26 around relay 122 at armature 127 so as to afford a better talking circuit. The talking current accordingly passes through condenser 125 and resistance 126 in multiple.

The calling and called subscribers may now converse with. each other as desired.

When the conve sation is completed, the two subscribers replace their receivers.

It will be assumed that the calling subscriber is the first to replace his receiver. When the receiver is replaced at the calling substation, line relay 3 of the connector O CG both fall back.

falls back and places ground as usual on the operating'circuit at armature 25, thereby closing a circuit as before for vertical magnet 15. Vertical magnet 15 is not operated at this time, however, on account of the fact that the relatively high resistance 16 has been inserted into the circuit in series with the vertical magnet 15 at armature 20 of switching relay 8. Series relay 5, however, operates in series with resistance 16' ahead of the ungrounding of conductor 97.

After the interval for which it is adjusted, release relay 4 falls back and opens the operating circuit and prepares a circuit for the release magnet 10 at armature 28. Series relay 5 does not fall back immediately, however, owing to the fact that it is slow acting. At armature 27, relay 4 removes ground from conductor 97, which, however. remains grounded at armature 21 of relay 17. At armature 26, relay 4 removes ground from release trunk conductor 95, thereby permit ting the preceding switches in the connection to be released in the usual and well known manner.

At the end of the interval for which it is adjusted, slow acting series relay 5 falls back and connects thegrounded holding conductor 97 to release trunk conductor 95 at armature 29, thereby rendering the connector C busy to the selector switches having access to it. The switches involved in the connection up to but excluding the connector C have now been released, but the connector C is maintained operated to main tain the trunk line TL busy at the main exchange end thereof, thereby maintaining the combined switching and cutoff relay 61 of the line switch LS operated so as to prevent the line switch LS from operating at this time.

When the called subscriber at substation A replaces his receiver, back bridge relay 2 of the connector C and the series supervisory control, relay 122 of the cord circuit Upon falling back, back bridgerelay 2 of the connector C, in addition to straightening out the connection between the incoming talking conductors and the windings of line relay 3, at armatures 24 and 23, opens the circuit of relay17 at armature 18, but relay 17 being slowacting, does not deenergize immediately.

In the branch exchange, the deenergization of series relay 122 results in relay 123 being bridged across the talking conductors of the. cord circuit again, this occurs,

'nector falls back due t 6 nesaeeo which adjustment, however, is not stiff the back bridge relay or? the cones or G enough to prevent its operation in response in the main exchange again pulls up in tothe ringing current projected out over Series with relay 123 in the cord circui C t line TL from the main exchange as which pulls up also. bridge re 2 aeiore pointed out.

of the connector C closes .l-e Kit th l l'llllu circuit TC, relay 103 now of the associated slow actinorelay 1? at OJl'tttQS anc arinigs its arnmuie 11.1 into the position i 17 has had time to fall back. count or: the

In the cord ircuit- CG, he energization necaiens .rnal ot' the batter conof relay 123 results in the removal the 1. t Accordingly, relay 103 opens u 1i A. .1: 1' v 1 resistance 126 rrom 111 shunt 0t relay 1:22 at r uit ow acting relay 10o armaarrnature 127 so as to enable relay 122 to tur 1 t that relay 195 deenergize again readily 111 case the lateral and dissubscriber is not finally hang'ng up ceiver but is merely attempting to local operator. As a further energization of relay 123, the supervisory lamp 121 is closed a. 128, whereupon the lamp 121 cm due-tor 117 from stead to cut-oil re- The trunk line 7 =1dition.

t the subscriber to converse with a.

' Will not:

:rtl cut 1.

lighted to inform the on. .tor that tl e subsubscribe mal and that scrlber at substation Jr has replaced his r he :c or 'eceiver and ceiver. a p

riber in the yes his rec cor cucr llllQ i i i which encrg' relay 1 see and plu P from the jack Q2, contacts 1 "rate 1 the circuit of r lay 10 1, eupon the" 10a falls back; opens one 1 t in the r cuit of relay 105 at zrmatu 11Sv th' relay 105 energized through armature 11;) :plr

and its Working contact; and at armature 112, opens the circuit of relay 02. l 102 accordingly falls back and connects the ring up Winding of relay 101 anl he polarized relay 103 across the conch? t trunk line TL.

' r r relay 21;, it connects o the iunction of switch atrre to be idle this relay 212 does not e icct at this tim and t W I 1, role, :11 enemy/lee. seizing tuc adjusted, slow acting relo circuit at armature 18, the connector C is released. cordingly removed from pri ductor d8 of the line swite 45, whereupon the combine.

on the other hand that he arch hing role v cut-oil relay 61 of tie line iauud potential back and connects ground If test contact by test and connects line t cr me In this is applied 7 contacts to loperates in a. 0 advance the Wipers .1 idle trunk.

1 It will be noted t rh bath tions to conductors and r opposite to the battery connection conductors prior to rel ase o lllltQfllGe Oil 12111111 e nector C. This quick reversal of the Y c connections to the conductors ot the s. reached, which line TL has a tendency to operate re ed, the one coin- Whose lower winding 18 connected and extending these conductors in eerie. wit'i the denser 117 of the trunk circuit TC. relay does not operate at this time on count of its relatively still adjustment,

uttered by test l if:

wiper 214, energizes in series with stepping magnet 226. Stepping magnet does not energize at this time on account of the relatively high resistance of switching relay 211. Upon energizing, switching relay 211 disconnects test wiper 214 from the junction of its own winding and that of stepping magnet 226 and connects it instead to the grounded private normal conductor 202, thereby making the seized trunk busy immediately; and at armatures 221 and 223 disconnects the line conductors from the winding of line relay 212 and ground and extends them by way of wipers 213 ant 215 to trunk conductors 216 and 218, respec-c tively, of the seized trunk. Responsive to this operation, the line and release relays of the-seized selector (notshown) operate and the latter places ground on the release trunk conductor 217, thereby establishing the usual holding circuit for the line switch LS before the slow acting line relay 212 has had time to fall back.

hen the calling subscriber manipulates his calling device in accordance with the digit necessary to obtain connection with the main exchange, the seized selector switch raises its wipers opposite the corresponding level of bank contacts and rotates them in search of an idle trunk In this case it will be assumed that the trunk line TL, which, among other trunks, is accessible to the local selectors through holding circuits (such as HC), is seized at bank contacts 146148. When this occurs, the seizing selector switch places ground on release trunk conductor 117 through the medium of bank contacts 147, thereby closing acircuit through armature 116 and its resting contact of relay 105 for cut-oft relay 102. Cutoff relay 102 accordingly pulls up and disconnects the ringup relay 101 and the polarized relay 103 from in bridge of conductors'47 and 49 at armature 110, Relay 103 deenergizes and the spring associated with armature 111 brings the said armature 111 into engagement with its associated contacts, but no circuit is closed for relay 105 at this time, owing to the tact'that the working contact of armature 111 is ungrounded at armature 109 of cut-oti' relay 102. The visual busy signal 119, in series with the visual busy signal at the night position, is energized in multiple with cut-off relay 102 so as to inform the operator at the day position that the trunk line TL is busy.

As a further result of the seizure of the trunk line TL by the local selector through the medium of the bank contacts associated with the holding circuit HO, the conductors of the calling line are extended to bank contacts 146' and 148 which are connected to conductors 4'7 and 49. Accordingly, line relay 62 of the line switch LSin the main exchange now energizes over the trunk line TL in series with relay 142 of the holding circuit HQ, with the result that relay 142 closes at armature 144 a circuit for relay 141 which pulls up and grounds conductor 117 at'armature 143 before the slow acting re lease relay of the seizing selector has had time to fall back.

In the main exchange, private normal Conductor 48 of the line switch LS is grounded in the usual manner by line relay 62. Also, the line switch LS seizes an idle first selector in the manner similar to that described in connection with the operation of the line switch LS in the branch exchange. Assuming that the first selector seized is the one reached by way of conductors 7875, this selector is prepared for operation in the usual manner and grounds the release trunk conductor 74, thereby closing the usual holding circuit for the line switch LS before the slow acting line relay 62 hashad time to fall back. I

The calling subscriber now manipulates his calling device in accordance with the directory number of the desired subscriber in the main exchange. with the result that the desired connectionis completed and the de sired subscribers bell is rung by the connector switch in the usual manner.

Relay 142 of the holding circuit HG responds to thedial but the slow acting relay 141 keeps the release trunk conductor 11? grounded.

lVhen the called subscriber responds, the ringing current is cut off by the connector in the usual manner and the talking circuit is completed, whereupon the two subscribers may converse with each other in the usual manner.

When the conversation is completed, the two subscribers replace their receivers. V

lVhen the receiver is replaced at substation A, the circuit of the linerelay of the connector in use is broken, as well as the circuit of the series relay 142 oi the hold-- ing circuit HO. Responsive to the deenergization ot the line relay of the connector in the main exchange, the switches in the main exchange, including the line switch LS are released.

Responsive to the deenergization of the series relay 142 of the holding circuit H0 in the branch exchange, the circuit of relay 141 is openedwith the result that this slow acting relay deenergizes utter an interval and removes ground "from release trunk conductor 117 at armature 143. When this occurs, the trunk line TL is rendered accessible to the local selector switches again and cutoff relay 102 of the trunk circuit TC, as well the visual busy signal 119 and the corresponding signal at the night position, deenergizes. The entire connection is now released.

In case the subscriber at substation A so back when she gets that number.

Assuming that this is done, the operator notes the condition 01' the various visual indicators, such as 119, at her position, and she takes the plugof an idle cord circuit, for zample, the plug 1 of the cord circuit CC and inserts it into the jack J. ihe closure of contacts 118 of the jack J results in the operation oi relay 101. Relay 10st closes at armature 112 a circuit tor cut-oil relay 102. at the same time placing ground on conductor 11? through the resting contact and armature 116. Relay 102 cuts the trunk circuit bridges oil from conductors a? and 9, whereupon relay 103 restores and closes a circuit "for relay 105 from alt-mature 113 and its working contact. Relay 105 energizes and disconnects conductor 117 from ground in multiple with relay 102 and the 'ual signals and connects it directly to und at armature 116;.closes a locking circuit for itseli at armature 115 independ ent of armature 113 and its working-contact; and at armature 11 i closes a point in the negative talking conductor.

lVhen the ne ative talking conductor is finally connected up, bridge is closed across conductors 47 and 19 which includes the tip and ring contacts or the jack 5, the corresponding contacts of the plug P, contacts ot the calling device key K, and the supervisory relay 123 which is bridged across the talking strands of the cord circuit CC through the contacts of relay 122. Relay 123 accordingly energizes in series with the line relay of the line switch LS on the distant end of the trunk line TL and closes a circuit for the supervisory lamp 121 at armature 128.

in the main exchange, the line switch LS operates in the usual manner and seizes an idle first selector.

The operator now throws the calling device key K, thereby disconnecting the tip and ring conductors of the plug P from the remaining part of the cord circuit and connecting them instead to the common calling device taps and 136which are connected together through the sending contacts of the calling device CD and the secondary windings of the operators induction coil.

The operator new manipulates her calling device CD in accordance with the digits in the ninnber ot the desired substation, with the result that the desired connection is completed in the usual manner.

After having communicated with the called so scriber and having told him to wait a few seconds, the operator inserts the plug P into the jack J and signals the subscriber at substation A.

neeaaso extinguishing the lamp 121 at armature 128 and shunting relay 122 by the resistance 126 at armature 127.

The calling and called subscribers may now converse with each other in theusual manner, and, when the conversation is completed, they both replace their receivers.

When the receiver is replaced at substation A, relay 122 falls back and again bridges relay 123 across the talking conductors, whereupon relay 123 pulls up and lights the lamp 121 and removes the resistance 126 trom in shunt of relay 122. Accordingly, if the subscriber at substation A raises his receiver again from the hook, relay 122 energizes again readily because it is not at this time shunted by resistance 126, and the lamp 121 is eminguished.

in case the subscriber at substation A desires to converse with the operator, he lowers and raises his switchhook several times, with the result that the lamp 121 becomes lighted and extinguished several times, attracting the attention of the operator who may throw her listening key and converse with the subscriber and carry out his desires.

lVhen the operator leaves her switchboard at the end of the business day, she operates the night key NK. thereby connecting the talking conductors of the trunk line TL to the attendants circuit at the ni ht position. The night key NK at its upper contact prepares a circuit for operating relay 104 from the night position, and at its lower contact disconnects armature 107 of ring-up relay 101 from the answering lamp 118 at the day position and connects it to the answering lamp 169 at the night position. Accordingly, all calls incoming to the branch exchange from the main exchange over the trunk line TL after the night key NK is thrown, are handled atthe night position. The attendant at the night position is not usually a regular operator but is, in many cases, a night watchman, or someone else holding a similar position. Accordingly, the night position is not equippedwith cord circuits as is the day position, but is equipped rather with a simple key circuit by means of which the night attendant may, upon answering a call, dial the local number of the desired subscriber, thereby extending the connection.

Assuming now that the night key NK is thrown and that the trunk line TL is seized by a connector in the main exchange, relay 103 falls back in the usual manner responsive to the seizure of the trunk line TL and closes a circuit for relay 105 which pulls up and makes the trunk line TL busy in the branch exchange.

When the ringing current is projected its lower contact of the night key NK for theanswering lamp 169 at the night position." The attendant at the night position, upon noting the lighted condition of the lamp 169, operates the answering key AK. The upper contact of the key AK closesa circuit through the upper contacts of the key Nlifor relay 10 1 which thereupon energizes and closes at armature 112 a circuit for cut-oft relay 102 which pulls up with the hereinbefore described results. As a further result of the operation of the key AK, it closes, at its sec ond pair of contacts from the bottom, a circuit for the polarizing winding of'the electropolarized relay 158. This winding is com posed of a comparatively small number of turns of wire having a relatively high resistance and it is, therefore, unable to operate the relay unassisted. At its springs connected with conductors 154,- and 155 the key AK connects these conductors to the talking conductors of the key circuit KC, thereby establishing a bridge through the impedance 156 for operating the ring cut-oft and back bridge relays (for example, relays 6 and 2 of the connector'C, Fig. 1) of the seizing connector. e

As a furtheri'esult of the operation of the key AK, a bridge is closed across conductors 162 and 163 at the middle contacts of the key AK which includes the back bridge impedance 157 and the upper winding of the electro-polarized relay 158. Accordingly, the

line relay of the line'switch LS energizes through this bridge with the result that the line switch LS seizes an idle selector switch in the usual manner. The direction of the current flow through the upper winding of the electro-polarized relay 158 is such that this winding assists the polarizing winding in operating the relay. .This relay closes at armature 159 a circuit'for the supervisory lamp 160, which accordingly becomes lighted.

The attendant now throws the key K into listening position, thereby connecting conductors160 and 161 to conductors'162 and 163.. Talking battery is supplied to the at tendants circuit AT (which is an ordinary automatic telephone with the ringer removed) in multiple with the bridge across the talking conductors including impedance 157. The attendant now converses'with the calling subscriber and ascertainsthe number of the subscriber with whom he desires to converse.

Assuming that'the called subscriber is still atjthe plant, the attendant throws the key K into its. opposite position, thereby connecting conductors 160 and 161 to con-t ductors 162 and 163 to the exclusion of'the holding bridge including the impedance 157. The attendant now operates the calling device CD" in accordance with the local number of the called branch exchange subscriber with the result that the connection is extended to his line in the usual manner.

- When the called subscriber responds, the connector switch in use reverses the direction 01": current flow in conductors 162 and 163.

lVhen this occurs, the lines of force produced by the upper winding of relay 158 oppose those produced by the lower winding of the relay and the relay retracts its armature 159,

mature 159 and lights the supervisory lamp 160.' WVhen the attendant sees this, he restores the key AK, thereby opening; the

bridge across the conductors 162 and163 and permitting the local switches to release. The release of the main exchange connection takes place in this case in the same manner that it took place in the preceding caseQ WVhat is claimed is: I y

1. In a telephone system, an automatic connector 'switch having line wipers and a test wiper, a line accessible to said connector switch, a line relay and a cut-ofi' relay for said line, a relay in said connector switch energized responsive to the idle condition of said line when the wipers are brought into engagement with the contacts thereof to close a circuit for said cut-off relay over said test wiper, and a second relay energized respoiisive to the energization of said first re-- lay to connect the line wipers to the connector switch. 1 i

2. In atelephone system, acord circuit having two talking strands and a guarding conductor, an open point in one of the strands of said cord circuit, a plug and a' jack for connectingsaid circuit to a line, a ringing key in said cord circuit, a relay operated by the ringing key to close the open point subsequent to the insertionof the plug into the jack, and contacts on said relay for closing. a locking circuit for itself independent of the ringing key but including said guarding conductor.

3. In a telephone system, a subscribers 7 line, a cut-off relay .in said switch, a cord circuit having a plug, a circuit excluding said plug 'for energizing said cut-off i'elay responsive to the insertion of said plug in circuit having a plug, a

said jack, a normally open bridge across the talking contacts of said plug, and means controlled by the operator after the plug is inserted for closing said normally open bridge.

L. In a telephone system, a subscribers line, a line switch and a jack individual to said line, a line relay in said switch respon sive to the closure of a bridge across said line, a cut-off relay in said switch, a cord circuit for energizing said cut-oil relay responsive to the insertion of said plug in said jack, a norinall open bridge across the talking contacts of said plug, a relay for closing said normally open bridge, means including a key i'or energizing said lastmentioned relay, and a locking circuit for holding said relay energized in parallel wit, said cut of. relay.

5. In a telephone system, a subscrihefis line, a line switch and a jack individual to said line, a line relay in said switch responsive to the closure of a bridge across said line, a cut-off relay in said switch, cord circuit having plug, circuit for energizing said cut-off r y responsive to the insertion of said plug in said jack, a normally open bridge across the ing contacts of said plug, a seltdocking relay for closing said normally open bridge, and a key for closing an initial. energizing circuit for said locking relay.

6. In a telephone system, a subscribers line terminating in a jack, a cord circuit having one contact of the plug normalh tree of battery or ground, a line switch for line having a line relay normally connected to the line conductor engaged by plug contact when the plug is inserted in said jack, a cutot't" relay energized when the plug is inserted in said iacl: to disconnect said line relay, and nreans controlled lay the operator after the plug is inserted for connect ,ing said plug contact to one pole of the battery. v

7. In a private branch exchange. day and ni ht operator s positions, a. trunk line incoming from a main exchange and terminating in a jack at said day position, a branch of said trunk line extending to said night position, a branch extension 7' through said night position to an automatic switch, a normally open key inserted hetween said trunk line and said branch at said day position, and a second normally open key inserted between said branch and the said extension at said night position.

8. In a private branch exchange. day and night operators positions, a trunk line incoming from a main exchange and tci int ing in a jack at said day position, a bench of said trunk line extending to said ht position, a branch extension exten ng through said night position to an automatic switch, a signal at said day position norinal- 1y responsive to a call over said trunk line,

nosenso a. normally non-responsive signal at said night position, and a key at said day position for rendering said first signal non-responsive and said second signal responsive.

9. in a private branch exchange, day and night operators positions, a trunk line incoming from a main exchange and terminating in jack at said day position, a branch. oi said trunk line extending to said night "ion, a branch extension extending ough. night position to an automatic tcli, subscribers lines in said branch exchange, inanual switching equipment for e tending calls from said jack to said lines when the day position is in use, and automatic switches cooperating with said first automatic s iteh to automatically extend calls from sait trunlr line to said lines when the night po ion is in use.

10. In a branch e change, day and night trons, a trunk l e haying ternnnals at 1 positions, trunl: signals at said pos for re. dering either o't said it) calls depending on A is in use, subscrihcrs lines, :e u connecting said trunk said lines when the day position in use, and aatonretic switches tor con- "ing said trnnl: line with said lines when re nigight position in us ll. i; one digit switchless rotary connector snitch connirising a magnet for directively operating it to select a group of trunks. a second magnet automatically re snonsi'rc the Cl es ation of the directive opitor automatically operating the select an idle trunk, a switching is found to co ncct the switch wipers d complete a circuit, a ring cutrelay con rolled the selected trunl: p and close the ra rng conductors, and a, back bridge relay for "feeding current to the selected trunk.

152. a release by party connector switch, a switclnng relay, a ring cut-oft relay, a. conductor torsupplying current to lock relays energized, an incoming release "1!)3' normally connected to said i c JCiOlJlllCfil .for operating and re no said switch, and means for scpan ing said conductors while the switch i3 1 released.

a release by last party"two-ino tion connector witch, a ring cut-otl relay, a switching relay. said relays being of the selfpe', a conductor tor supplying Clll"i' 3ilt to the locking windings of said re lays, an inco. rig release trunk conductor normally (it. ected to said locking con- I change-over relay, and contacts on said change-over relay forseparatinpi conductors.

for, a back bridge relay, a slow acting relay, means for energizing said first relay "while the slow acting relay is deenergized, means controlled by said first relay when energized for energizing saidslow acting relay, and contacts on said slow relay for opening said circuit.

15. In an automatic switch, line wipers and a test wiper, said line wipers being normally disconnected from the talking con ductors of said switch, operating means for said switch, relay energized responsive to the completion of the operation of said switch, a second relay energized responsive to the energization of said first relay, contacts on said first relay for placing a potential on said test wiper, and contactson said second relay for connecting up said line wipers. r

16. In a telephone system, two serially related switches for setting up a connection, a-release trunk conductor extending between said switches, a local test conductor in the second switch normally connected, to

said release conductor, means independent of the calling party for applying a holding potentialto said local testconductor, and means controlled by the calling party for separating said conductors to release said first switch. a

17. In a telephone system, a calling and a called line, automatic switches, a connector, means for operating said switches and connector to complete a connection between the said lines, a back bridge relay in said con-i nector controlled by the called party, means in said connector for establishing a holding circuit to hold said switches in their operated positions, means responsive to the calling subscriber hanging up his receiver for opening said holding circuit to permit said switches to release to normal, and a slow acting relay controlled by said back bridge relay to prevent the release of said connector and to make the connector busy to switches having access thereto.

18. In a telephone system, a single digit rotary connector switch having directive primary and automatic secondary movements, means for operating said switch inits directive primary movement to select a group of lines, a change-over relay in said switch energized during the primary move-* ment and deenergized responsive to the completion thereof for auton'iatically starting 'said secondary movement to select an idle line in the group, a guarding conductor for said switch having guarding potential connected thereto independent of control of the calling line, and means controlled by said change-over relay for momentarilyremoving guarding potential from said guarding conductor responsive to the calling party hanging up his receiver before the called party.

of lines, a change-over relay in said switch energized during the primary movement and 'deenergized responsive to the completion thereof for automatically starting said sec-' ondary movement to select an idle line in the group, a back-bridge relay in said switch for feeding talking battery to the called line,

a guarding conductor for said switch having guarding potential connected thereto inde- V pendent-oi: control of the callin line, means controlled by said change-over relay for momentarily removing guarding potential from said guarding conductor responsive to the calling party hanging up his receiver before the called party, and means controlled by said back-bridge, relay for: thereafter maintaining guarding potential on said guarding conductor until the called party hangs up his receiver.

20. In a telephone system, a calling line, a called line, automatic switches, a connector,

an operators position, a trunk line accessible to said connector and terminating in a jack at said position, means controlled by the calling subscriber for operating said switches and connector to extend a connection to said trunk, a cord circuit for connecting with said jack to complete the connection to the called line, a back-bridge relay in said connector controlled by the called subscriber, means in said connector controlled by the calling subscriber for establishing a holding circuit for said switches and connector, means for releasing said switches to normal responsive to the calling subscriber hanging up his receiver, means for operating said back bridge relay responsive to the called subscriber hanging up his receiver, means in said cord circuit for again operating said back bridge relay, and a relay controlled by said back bridge relay for controlling the release of said connector and for making said connectorbusy to switches having access thereto until said cord circuit is removed fromsaid switching relay for connecting said talking conductors to said line wipers. 22. In a telephone system, a first exchange,

ill)

ly connected branches of said trunk termiynatlng in automatic switches a said ,at the second exchange, me

2. second exchange, a two way two conductor trunk connecting the two exchanges, normale automatic swi -h and a 3 1 l chage and in an i for enrol-e 'nal, a superv iii-.ing the operat contacts no finally closing a shunt circuit around relay: said supervisory relay connector; n idge ol said two talking conductors, and contacts on Said first relay included in the bridge circuit of said supervisory relay.

2%. In a telephone system, a calling; line,

a called line, autor tic switches, a connector,

signal and h avin an operators position, a trunk line accessible to said connector and terminating in a jack at said position, means controlled by the calling subscriber for operating said switches and connector to extend a connection to said trunk, a cord circuit'for connecting with said jack to complete the connection to the called line, n'ieans for releasing said switches to normal responsive to the calling subscriber hanging up his receiver, a back bridge relay in said connector controlled by the called subscriber to prevent the release of the connector, said back bridge relay being deenergized when the called subscriber hangs up, means in said cord circuit for again operating saidback bridge relay, a slow acting relay controlled by said back lin'idgge relay for preventing the release 01. the connector during the interval that the said back bridge relay is dcenergized, and means controlled by the slow acting relay for making said connector busy to switches having access thereto until said cord circuit is removed from said aclr;

In witness whereof, I hereunto subsc lbc in name this 20th day of January, A. 1).,

oor

CLARENCE E. ROMA 

